This kind of industrial robot has hitherto been so constructed that, for example, as shown in FIG. 17, at an intermediate portion of an arm E or manipulator supported to a base S are provided three first, second and third rotational joints R.sub.1, R.sub.2 and R.sub.3 rotatable around the shaft extending lengthwise of the arm E and three first, second and third bending joints P.sub.1, P.sub.2 and P.sub.3 swingable around the shafts perpendicular to the longitudinal direction of the arm E, these joints being disposed from the base S to the utmost end of the arm E in the order of the first rotational joint R.sub.1, first bending joint P.sub.1, second bending joint P.sub.3, second rotational joint R.sub.2, third bending joint P.sub.3, and third rotational joint R.sub.3.
The first through third rotational joints R.sub.1, R.sub.2, and R.sub.3 rotate around the shaft at the arm E and the first through third bending joints swing around the shafts perpendicular to the arm E respectively, thereby controlling the position and attitude of a working machine mounted on the utmost end of the arm E for carrying out various works.
For the convenience of explanation, in a robot shown in FIG. 17, a portion extending from the base S to the first bending joint P.sub.1 is called a trunk A, that from the first bending joint P.sub.1 to the second rotational joint R.sub.2, an elbow B, and that from the second rotational joint R.sub.2 to the utmost end of arm 2, a wrist C.
The trunk A can rotate its upper half portion with respect to its lower half portion through the first rotational joint R.sub.1, the elbow B can change its angle with respect to the trunk A and an angle of the rear half portion of the elbow B with respect to the front half portion thereof, and the wrist C can obtain three degrees of freedom by the second rotational joint R.sub.2, third bending joint P.sub.3 and third rotational joint R.sub.3, so that the utmost end of the arm E can obtain six degrees of freedom, whereby the working machine is controllable accurately of the position and attitude thereof by the six degree of freedom.
In this case, however, the trunk A, elbow B and wrist C, when the utmost end of arm E is controlled, is somewhat restricted.
In detail, when the utmost end of the arm E is fixed in the position and direction, the elbow B, even when intended to move, is restricted by the first and second bending joints P.sub.1 and P.sub.2 to result in that a change in an angle of the elbow B with respect to the trunk A and that between the front half portion at the elbow B and the rear half portion thereof are not at all performable. Moreover, it is quite impossible to bring down the elbow B to change its height. In brief, in a case where two or more bending joints P.sub.1 and P.sub.2 are continued and no rotational joints are provided therebetween, the elbow B, when the utmost end of the arm E is fixed in the position and direction, is restricted in motion, whereby it is impossible to desirably swing the elbow B in the three dimensional space.
Accordingly, the working machine at the utmost end of the arm E, when inserted into a narrow work space to carry out various works, is restricted thereto.
For example, when a welder mounted on the utmost end of the arm E, as shown in FIGS. 18 and 19, is inserted into an automobile through a door D for carrying out a welding work therein, even if an obstacle, such as a door frame F, is in front of the inserted arm E, it is quite impossible to change the height of the elbow to avoid the obstacle. After all, an intermediate portion of the arm E comes into contact with the obstacle, thereby making impossible the insertion of the arm E into the automobile.
Therefore, in the aforesaid industrial robot, as shown in FIGS. 18 and 19, a service rail SR is provided in parallel to the assembly processing line for the automobile and the base S is slidably supported to the service rail SR, so that the base S is slide from one lengthwise side of the service rail SR from the other side, and the arm E is inserted into the automobile while sequentially controlling the position and attitude of the arm E as shown sequentially in the drawings.
However, such service rail SR, when used for various works, is expensive to install and requires a large installation space.